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Atmosphere and Climate Change
Section 1
Climate
• average weather conditions in an area over a long period
of time.
• determined by factors that include: latitude, atmospheric
circulation patterns, oceanic circulation patterns, the
local geography of an area, solar activity, and volcanic
activity.
• most important factor: distance from the equator
Atmosphere and Climate Change
Section 1
• Latitude: distance north or south from the equator, is
expressed in degrees
• Equator at 0° latitude, most northerly latitude is the
North Pole, at 90° north; most southerly latitude is the
South Pole, at 90° south
• affects climate because the amount of solar energy an
area of the Earth receives depends on its latitude.
Atmosphere and Climate Change
Section 1
Low Latitudes (near equator)
• more solar energy falls on these areas
• night and day both about 12 hours year-round
• temperatures high year-round, no summers or winters
Atmosphere and Climate Change
Section 1
High Latitudes (closer to poles)
• sun is lower in the sky, reducing the amount of energy
arriving at the surface
• sunlight hits the Earth at an oblique angle and spreads
over a larger surface area than it does at the equator
• temperatures lower than they are at the equator
Atmosphere and Climate Change
Section 1
• hours of daylight vary
• 45° N and S, as much as 16 hours of daylight during the
summer ; 8 hours of sunlight in the winter
• Near poles, sun sets for only a few hours during the
summer, rises for only a few hours during the winter
– yearly temperature range very large
Atmosphere and Climate Change
Section 1
Atmospheric Circulation
• Air circulation affects climate
• Cold air (denser than warm ) sinks, compresses and
warms
• Warm air rises, expands and cools
• Warm air can hold more water vapor than cold air
can. When warm air cools, the water vapor it
contains may condense to form rain, snow, or fog.
Atmosphere and Climate Change
Section 1
• Solar energy heats the ground, warms the air above
• Warm air rises, cooler air moves in to replace it. This
movement is called wind.
• Earth’s rotatation, energy differences N & S create
pattern of global atmospheric circulation
– circulation pattern determines precipitation pattern
Atmosphere and Climate Change
Section 1
• Ex: intense solar energy at the equator causes the
surface and air above to become very warm
– warm air can hold large amounts of water vapor
– as it rises and cools, its ability to hold water is
reduced, producing large amounts of rain
Atmosphere and Climate Change
Section 1
Global Circulation Patterns
• Cool air over the equator cannot descend because hot
air is rising up below it.
• Forced away, accumulates at about 30º N & S
– Some sinks becomes warmer. This warm, dry air then
moves across the land, causes water to evaporate
from the land, creating dry conditions.
Atmosphere and Climate Change
Section 1
• At about 60º N & S air from equator air collides with cold
air from the poles
– the warm air rises, most forced toward the poles
– cold, dry air descends
– poles essentially very cold deserts
Atmosphere and Climate Change
Section 1
Prevailing Winds, (Belts)
• Winds that blow predominantly in one direction
throughout the year
• Because of the Earth’s rotation not directly northward or
southward
– deflected right, from northeast, Northern Hemisphere
– deflected left, from southeast, Southern Hemisphere
Atmosphere and Climate Change
Section 1
• Belts produced between 30º N & S latitude and the
equator, trade winds
• Belts produced between 30º and 60º N & S, westerlies
• Belts produced between poles to 60º N & S, easterlies
Atmosphere and Climate Change
Section 1
Oceanic Circulation
• Ocean currents have a great effect on climate because
water holds large amounts of heat.
– surface currents caused mostly by winds, Earth’s
rotation
– redistribute warm and cool masses of water around
the world
Atmosphere and Climate Change
Section 1
El Niño–Southern Oscillation (ENSO)
• El Niño: warm phase
• periodic occurrence in eastern Pacific Ocean when
surface-water temperature becomes unusually warm
• winds in the western Pacific Ocean, strengthen, push
warm water eastward
• rainfall increased southern half of U.S., drought in
Australia.
Atmosphere and Climate Change
Section 1
• La Niña: cool phase
• periodic occurrence in the eastern Pacific Ocean when
surface water temperature becomes unusually cool
• El Niño and La Niña are opposite phases of cycle.
Atmosphere and Climate Change
Section 1
Pacific Decadal Oscillation (PDO)
• Long-term, (20 to 30 year) change in location of warm
and cold water masses in the Pacific Ocean
– influences climate in the northern Pacific Ocean, N.A.
– affects ocean surface temperatures, air temperatures,
and precipitation patterns
Atmosphere and Climate Change
Section 1
Topography
• Height above sea level (elevation) has an important
effect on climate.
• Temperatures fall by about 6°C (about 11°F) for every
1,000 m increase in elevation.
• Mountain ranges also influence the distribution of
precipitation.
– rain on the western side, eastern side dry
– effect known as a rain shadow.
Atmosphere and Climate Change
Section 1
Other Influences on Earth’s Climate
• At a solar maximum, increased amount of ultraviolet
(UV) radiation
– produces more ozone, which warms the stratosphere
– can also warm the lower atmosphere, surface a little
• Large-scale volcanic eruptions produce sulfur dioxide
gas that can reach the upper atmosphere.
– can remain in the atmosphere for up to 3 years
– reacts with water vapor and dust to form a bright layer
of haze that reflects enough sunlight to cause a
global temperature decrease
Atmosphere and Climate Change
Section 1
Seasonal Changes in Climate
• The seasons result from the tilt of the Earth’s axis, about
23.5° relative to the plane of its orbit
– the sun’s rays strike the Earth at different angles as
the Earth orbits the sun
Atmosphere and Climate Change
Section 1
Seasonal Changes in Climate
• Summer, Northern Hemisphere, earth tilts toward the
sun and receives direct sunlight.
– hours of daylight greatest
– Southern Hemisphere tilts away from the sun,
receives less direct sunlight (their winter)